Without wanting to sound hard-nosed about it, Mike and I tend to build tools that we want to use ourselves. Neither of us are big fans of threaded discussion boards, so our motivation to do it really well would probably not be 100%, and as a result it would likely not be developed to the exacting and meticulous standards that we apply for the rest of the features. As a result, it's probably best to concentrate solely on what we do use and make it as good as possible, which means that as Mike said, I would not expect to see threaded mode appear as an option in XenForo any time soon.